The invention relates to an apparatus and method for measuring strength related characteristics of a part using x-ray diffraction techniques and, more particularly, to an apparatus and method for measuring the strength related characteristics at a variety positions on the part.
The use of x-ray diffraction techniques for measuring residual stresses in crystalline substances such as metal or ceramic materials is well-known. The general idea with the use of x-ray diffraction is to subject the material to the radiation of x-rays with the resulting sensed x-ray diffraction peak interpreted to arrive at a measurement of a strength related characteristic, i.e. stress, retained austenite, hardness of the part material, to show, for instance, the level of fatigue in the material. While using coupons or removing the part from service for measurement by x-ray diffraction laboratory equipment is done, neither is particularly satisfactory in that coupons require a portion of the part to be removed therefrom, and removing a part to be measured from service can create undue downtime along with the requisite labor for removal and replacement of the part back into service.
Accordingly, there is a need for portable x-ray diffraction equipment that can be used in the field at the site at which a part is located and without requiring the part to be removed from service. Portable x-ray diffraction equipment is known, however, some of these units suffer from great bulk making them less than ideal for use in field conditions. A further shortcoming with known x-ray diffraction equipment lies in the limitations in moving the goniometer head so that measurements can be taken across a sufficient number of positions on the part to obtain meaningful information therefrom, particularly where the part being tested has been used in the field where corrosion and other environmental use conditions can cause highly localized variations in the strength characteristic being determined. When the only measurements taken are those including such localized aberrations, the determination of what the remaining useful life of the part is before it needs to be retired to avoid fatigue failure thereof can be compromised.
In the laboratory setting this shortcoming requires periodic operator intervention to shift the part being measured so that the goniometer head is in position to direct x-rays at different positions thereon. As is apparent, such operator intervention is time consuming and labor intensive. In the field with current portable units, an operator generally has to physically shift the x-ray diffraction unit including the goniometer head along the part to the different positions at which measurements are desired. In either instance, there is significant operator intervention that is required which is undesirable. In addition, a portable x-ray diffraction unit is needed that can take measurements from complexly-shaped, parts and preferably without having to remove them from service while also providing an easy to interpret readout of the results of the measurements to show variations in the fatigue of the part in the region thereof that is measured.
In this regard, currently there is no means available to directly and quantitatively measure the total strain and hence be able to calculate the total stress non-destructively, the dead load strain and hence the dead load stress on the following: wire rope and/or single strand and/or multi-strand cables once they are installed on a structure or component. In addition there is no technique which can determine the strains on individual strands which may comprise a cable bundle or wire rope.
It would be desirable to be able to measure the total strain and hence determine the total stress on these types of load bearing members. Total strain is the residual strain plus the restraint strain plus the applied strain. Accordingly, the total strain relates to a material""s remaining capacity to bear a load which is information that is particularly useful for load bearing structures for a number of safety and economic reasons.
Similarly, it would be desirable to be able to measure the dead load strain and hence dead load stress, which is the strain as a result of the weight and restraint stain of the structure or component without the strain due to the intended carrying load.
Another problem is that currently there is no means available to directly, accurately and non-destructively track the changes in wire rope and cable strain due to corrosion, creep, fatigue, overload etc.
A further problem is that currently there is no means available to directly and quantitatively and non-destructively measure the strain and hence be able to calculate the stress on the following: wire rope and or single strand and or multi-strand cables installed on an existing structure or component.
Despite the widespread use of cables, there are few tools available to inspect and characterize the stresses on cables. In fact, at this time there are two techniques currently in common use, a direct measurement by xe2x80x9cjackingxe2x80x9d, literally by deflecting the cable with a calibrated jack and an indirect method using the xe2x80x9ctime to dampingxe2x80x9d of an induced vibration. Both of these approaches to stress measurement are at best an approximation of cable force due to underlying assumptions as discussed in F. A. Zahn and B. Bitterli""s paper xe2x80x9cDevelopments in Non-Destructive Stay Cable Inspection Methodsxe2x80x9d delivered at the IABSE Symposium in San Francisco in August, 1995 (see pp. 861-866). This is because the accuracy of the measurement is less than ideal, the total stress in the cable is ignored and the techniques cannot characterize individual strands which may comprise a cable bundle. Accordingly, there is a need for an apparatus and method that can address these shortcomings.
In accordance with the present invention, an x-ray diffraction apparatus and method are provided in which an x-ray or goniometer head can be adjusted in different directions to allow the head to direct x-rays at a part from various positions. In this manner, measurements can be taken from a wider region of the part without requiring that the part itself be moved or that an operator move the unit, which can be relatively heavy. In one aspect, the head can be rotated about its internal axis so that it can more readily direct x-rays along curved surfaces of parts while keeping a substantially constant distance therefrom. It is preferred that the apparatus be a portable unit including adjustment mounts to allow the x-ray head to be moved in the different directions so that it can be transported for use in the field at the site at which a part is located. In this instance, the unit allows for measurements to be taken from the part while it remains in service. Accordingly, the present portable unit allows for x-ray diffraction techniques to be used on parts where it is not practical or economic to remove them from service, such as cables or wire ropes used as tension members for bridges. Moreover, the preferred portable x-ray diffraction unit herein provides an easy to interpret readout of the results of its measurements by generating a map at the part site so that, for example, any abnormalities in stress measurements taken will be highlighted in comparison to adjacent points on the map where more normal measurements are shown.
In one form of the invention, an apparatus is provided having an x-ray head adjustable in at least three mutually transverse axes for directing x-rays from different positions toward a part. The apparatus includes a frame for supporting the x-ray head. An x-axis adjustment mount of the frame is provided and which is operably connected to the head for adjusting the head in an x-axis fore and aft direction. A y-axis adjustment mount of the frame is provided and which is operably connected to the head for adjusting the head in a y-axis lateral direction. A z-axis adjustment mount of the frame is provided and which is operably connected to the head for adjusting the head in a z-axis vertical direction. Accordingly, the present x-ray diffraction apparatus is significantly improved in terms of its ability to coordinate movements of the head in three different axes of movement so that it can scan across a region of a part and direct x-rays thereat from different positions for taking measurements at a larger range of positions on the part than had been available via prior x-ray diffraction equipment. As the adjustment mounts are preferably integrated with the frame that supports the x-ray head, there is little need for operator intervention to move the part to reach the different points thereon from which measurements are desired to be taken.
In one form, the frame includes a fixture portion that is adapted to removably attach the frame to the part to allow the x-ray head to be used on parts in the field. With the fixture portion attached to the part to be measured, an operator merely has to initialize the x-ray diffraction unit for taking the desired measurements and otherwise need not intervene during the operation of the unit. This is in contrast to prior art x-ray diffraction equipment which requires an operator to hold the unit in position with respect to the part while the measurements are taken.
In another form, the fixture portion includes adjustable clamps for removably attaching the frame to different sizes of cables with the adjustable clamps comprising the y-axis adjustment mount to allow the head to be located at different positions along the length of the cable. The adjustable clamps for the fixture portion are advantageous as they do not require a different fixture to be constructed for each different part that is to be measured. Instead, the adjustable clamps can be used on cables of a variety of sizes for attaching the frame thereto.
In one form, the x, y and z adjustment mounts include linear drives for linearly adjusting the head in three mutually perpendicular directions with the x and y adjustment mounts allowing the head to direct x-rays to a predetermined region on the part and the z adjustment mount allowing the focal distance of the head from the part to be adjusted.
In another form, the frame and x, y and z adjustment mounts are integrated in a portable x-ray diffraction unit for being transported to different part sites. A stand distinct from the portable unit is provided for supporting the unit a desired part site. The integrated portable x-ray diffraction unit herein allows for measurements to be taken from parts in the field and from different points on the part by way of the integrated adjustment mounts.
It is preferred that the unit and the stand have an adjustable attachment therebetween to allow the unit and stand to be shifted to different positions relative to each other.
In a preferred form, the head includes detectors for sensing the x-rays off from the part. A controller is provided connected to the head for receiving signals from the detectors and including circuitry adapted to generate maps of a strength related characteristic of the part at the part site with the strength related characteristic being based on the received signals.
In another form, the head includes an elongate housing having a longitudinal axis, and the frame includes an r-axis adjustment mount operably connected to the head for adjusting the head in an r-axis rotary direction about the housing axis to allow the head to direct x-rays at contoured parts. Preferably, the frame includes a phi-axis adjustment mount operably connected to the head for adjusting the head in a phi-axis rotary direction transverse to the r-axis rotary direction. The phi-axis adjustment mount can be disposed forwardly in the x-axis direction from the z-axis adjustment mount.
In a preferred form, a touch sensor is provided which is shifted into engagement with the part with the head a predetermined distance from the part in the z-axis direction. A controller is signaled by the touch sensor for repeatable locating of the head at the predetermined distance from the part after use of the sensor. Preferably, the controller includes a teach mode to allow and operator to shift the touch sensor into engagement with the part at various locations thereon by shifting of the head via the adjustment mounts for mapping part contour so that the head precisely directs x-rays toward the part at the various locations along its contour.
In another form of the invention, an apparatus is provided for directing x-rays at parts with curved surfaces. The apparatus includes an x-ray head having an elongate housing including a longitudinal axis thereof, and a frame for supporting the x-ray head. An adjustment mount of the frame allows the head to undergo rotary movement about the longitudinal axis thereof to substantially keep the head at a predetermined distance from a curved surface of a part at which x-rays are directed at various positions along the part curved surface. Prior x-ray diffraction equipment has been limited to taking measurements from flat, planar surfaces. Where the part includes a curved surface, an operator would have to physically shift or rotate the part to allow the x-ray head to direct x-rays at different positions therealong. In contrast, the present apparatus including the adjustment mount for rotating the head about the housing axis allows the head to take measurements at various positions along the part curved surface while maintaining a substantially constant distance therefrom.
Preferably, a plurality of other adjustment mounts are provided for moving the head in a plurality of different directions so that the head moves in a path that substantially matches the contour along the part defined by the different positions at which x-rays are to be directed. As described more fully hereinafter, the contour of the part can be mapped into the memory of the controller which can then coordinate the operation of the adjustment mounts to allow the head to move in a path that keeps it at constant distance from the part despite complex shapes of its contour that may be present.
In another aspect of the invention, a method for obtaining strength related characteristics of a part is provided. The method includes providing a portable x-ray diffraction unit including an x-ray head having integrated adjustment mechanisms for shifting the head in a plurality of different directions, transporting the portable unit to a site at which the part is in service, orienting the x-ray head relative to the part for directing x-rays thereat, shifting the x-ray head via the adjustment mechanisms to direct x-rays at various positions on the part for obtaining a sufficiently large distribution range of measurements of the desired part characteristics for proper strength analysis thereof, detecting the diffraction of the x-rays from the part at the various positions thereon, transmitting signals to a controller for the portable unit that are based on the detected x-rays, interpreting the signals in circuitry of the controller to render measurements of at least one strength related characteristic of the part, and generating a map at the part site of the part characteristics across the entire distribution range of measurements for the part.
By generating maps at the part site, a person can readily determine the areas of the measured region where the strength related characteristic is in either normal or abnormal ranges therefor. The present method using an x-ray head having integrated adjustment mechanisms and which is incorporated in a portable x-ray diffraction unit makes it possible to generate the maps on site at a part location.